The government argued that it could trigger Article 50 using
royal prerogative, an ancient legal device which would have
allowed May to trigger the formal exit process without consent
from the House of Commons or House of Lords. She was
defeated, however, by a group of claimants led by investment
banker Gina Miller.

The government announced that it will appeal the decision, which
means the case is automatically referred to the Supreme Court,
the highest in the country — and that is where George Peretz QC,
a specialist in EU law, says the ECJ could become involved.

There would be a huge degree of irony if a key decision on Brexit
ended up being referred to EU's highest court.

Peretz, whose legal chambers has represented some of the
claimants in the case, told Business Insider how it could
happen:

1. In the High Court case, the government agreed
to the claimants' argument that Article 50 is
irrevocable — meaning that once it has been
triggered, it cannot be undone, and Britain has no choice but to
leave the EU within two years.

2. Peretz said that the government agreed with
this because "for political reasons, the government didn't want
to hint that it might be revocable." If the government had
suggested that Article 50 was revocable, it could have triggered
outrage from Brexiteers, including members of Theresa May's own
cabinet.

3. However, the government's lawyers might
decide to retract their argument that Article 50 is irreversible
when the case reaches the Supreme Court, in order to strengthen
their case. If they decide to argue the opposite — that the exit
process is revocable— then the
government would be able to argue that there is not as much need
for parliamentary approval before the article is triggered, as it
could be reversed at any point.

4. If the government does decide to make that
argument, then the two sides of the legal case would be in direct
disagreement over the interpretation of a piece of EU law —
Article 50. In that instance, the Supreme Court would be forced
to refer the case to the ECJ. Peretz explained that "if there is
a question of European Union law [in a Supreme Court case] they
have to refer it to the ECJ, unless the answer
is obvious. That's a basic principle of EU law."

5. Peretz believes the case is "unlikely" to go
to the ECJ, however. That is because he thinks the High Court's
ruling is still sound regardless of whether or not Article 50 is
reversible — he doesn't personally believe the case will "turn"
on Article 50 question.

He said: "The High Court's ruling still works even if the Prime
Minister could change her mind about triggering Article 50
eighteen months down the line."

In other words, the High Court's finding that the prime minister
does not have the right to use the royal prerogative is still
sound, whether or not she would be able to reverse article 50
further down the road.

Nick Barber, associate professor of Constitutional Law at Oxford
University,
told The Independent that it was possible the case would be
referred to the European Court of Justice, but added it was "very
unlikely."

Speculation that Theresa May would be able to "appeal" to the ECJ
should she lose in the Supreme Court was dismissed by the FT's
legal correspondent, David Allen Green, this afternoon:

For completeness, joking aside, May cannot appeal to ECJ if she loses at Supreme Court. Matter for judges whether to refer. Not likely here.